Process for the conversion of heavy charge stocks such as heavy crude oils and distillation residues

ABSTRACT

Process for the conversion of heavy charge stocks selected from heavy and extra-heavy crude oils, distillation residues, heavy oils from catalytic treatment, thermal tars, bitumens from oil sands, carbons of different origins and other high boiling charges of a hydrocarbon origin known as “black oils”, by means of the combined used of at least the three following process units: solvent deasphalting (SDA), hydroconversion with slurry phase catalysts (HT), distillation or flash (D), characterized in that it comprises the following steps: sending the heavy charge stock to a deasphalting section (SDA) in the presence of solvents, obtaining two streams, one consisting of deasphalted oil (DAO), the other containing asphaltenes; 
         mixing the stream consisting of deasphalted oil (DAO) with a suitable hydrogenation catalyst precursor and sending the mix obtained to a hydrotreating reactor (HT), introducing, into the same reactor, hydrogen or a mix containing hydrogen and H 2 S; sending the stream containing the product of the hydrotreatment reaction and the catalyst in dispersed phase to one or more distillation or flash (D) steps, by means of which the most volatile fractions are separated, among which the gases produced in the hydrotreatment reaction, from the distillation residue (tar) or from the liquid coming from the flash unit; recycling of at least a portion of the distillation residue (tar) or the liquid coming from the flash unit, containing catalyst in dispersed phase, rich in metal sulphides produced by de-metallization of the charge and possibly coke, to the hydrotreating section (HT).

The present invention relates to a process for the conversion of heavycharge stocks, among which heavy crude oils, bitumens from oil sands anddistillation residues, by means of at least three process units:deasphalting, hydroconversion of the charge stock using phase-dispersedcatalysts and distillation.

The conversion of heavy crude oils, bitumens from oil sands andpetroleum residues into liquid products can be substantially effected intwo ways: an exclusively thermal one and the other by means ofhydrogenating treatment.

Current studies are mainly directed towards hydrogenating treatment, asthermal processes create problems relating to the disposal of theby-products, such as, in particular, coke (obtained in amounts evenhigher than 30% by weight with respect to the charge stock) and to thepoor quality of the conversion products.

Hydrogenating processes consist of treating the charge stock in thepresence of hydrogen and suitable catalysts.

The hydroconversion technologies which are at present on the market, usefixed or ebullated bed reactors and make use of catalysts generallyconsisting of one or more transition metals (Mo, W, Ni, Co, etc.)supported on silica/alumina (or equivalent material).

Fixed bed technologies have several problems in treating particularlyheavy charge stocks, containing high percentages of hetero-atoms, metalsand asphaltenes, as these contaminants lead to a fast deactivation ofthe catalyst.

Ebullated bed technologies have been developed and commercialized fortreating these charge stocks, which give interesting performances butare complex and costly.

Hydrotreating technologies using dispersed phase catalysts can representan interesting solution to the drawbacks of the fixed and ebullated bedtechnologies. Slurry processes, in fact, combine the advantage of a highflexibility on the charge stock with high performances in terms ofconversion and upgrading, proving, at least in principle, to be simplerfrom a technological point of view.

Slurry technologies are characterized by the presence of catalystparticles having very small average dimensions and suitably dispersed inthe medium: for this reason the hydrogenation processes are easier andimmediate in all parts of the reactor. The formation of coke isconsiderably reduced and the upgrading of the charge stock is high.

The catalyst can be introduced as powder with sufficiently reduceddimensions (U.S. Pat. No. 4,303,634) or as an oil-soluble precursor(U.S. Pat. No. 5,288,681). In this latter case, the active form of thecatalyst (generally the metal sulphide) is formed in situ by thermaldecomposition of the compound used, during the reaction itself or aftersuitable pretreatment (U.S. Pat. No. 4,470,295).

The metal components of the dispersed catalysts are normally one or moretransition metals (preferably Mo, W, Ni, Co or Ru). Molybdenum andtungsten have much more satisfactory performances with respect tonickel, cobalt or ruthenium, and even more with respect to vanadium andiron (N. Panariti et al., Appl. Ctal. A: Gen. 2000, 204, 203).

Even if the use of dispersed catalysts solves most of the problems ofthe technologies described above, it has drawbacks mainly due to thecatalyst life and to the quality of the products obtained.

The way these catalysts are used (type of precursors, concentrations,etc.) are extremely important both from an economical and environmentalpoint of view.

The catalyst can be used at a low concentration (a few hundred ppm) inthe “once-through” mode, but in this case the upgrading of the reactionproducts is generally unsatisfactory (N. Pnariti et al., Appl. Ctal. A:Gen., 2000, 204, 203 and 215). If very active catalysts are used (forexample, molybdenum) and with higher catalyst concentrations (thousandsof ppm of metal), the quality of the product obtained is certainlyhigher, but it is necessary to effect the recycling of the catalyst.

The catalyst at the reactor outlet can be recovered by separation of theproduct obtained from the hydrotreating (preferably from the bottom ofthe distillation column downstream of the reactor) through conventionalmethods such as, for example, decanting, centrifugation or filtration(U.S. Pat. No. 3,240,718; U.S. Pat. No. 4,762,812) which are, however,extremely complex if applied to heavy charge stocks rich in poisoningsubstances.

As far as the chemical description of the conversion processes isconcerned, it is very useful to introduce the stability concept which,for a crude oil or an oil residue, expresses its tendency to precipitatethe asphaltene component due to a change in the operative conditions orin the chemical composition of oil and/or asphaltenes (incompatibility)following dilution with hydrocarbon cuts or chemical transformationinduced by cracking processes, hydrogenation, etc. . . .

Conventionally, asphaltenes are hydrocarbons which can be precipitatedfrom a crude oil or an oil residue, by treatment with a paraffinichydrocarbon with a number of carbon atoms ranging from 3 to 7, forexample n-heptane under the standard conditions provided for by theregulation IP-143.

From a quality point of view, it can be asserted that incompatibilityphenomena occur when products having very different characteristics withrespect to the nature of the malthene component, i.e. the non-asphaltenecomponent, are mixed, as in the case of the mixing of paraffinic crudeoils with aromatic oils, or the dilution of oil residues with cutterstocks of a paraffinic nature (a typical case is the fluxing of tarsfrom visbreaking with low aromatic gas oils).

In conversion processes of oil residues, bitumens from oil sands andheavy crude oils to distillates, the maximum conversion level is limitedby the stability of the residue produced. These processes, in fact,modify the chemical nature of oils and asphaltenes causing a progressivedecrease in stability with an increase in the severity level. Over acertain limit, the asphaltenes present in the charge can give rise to aphase separation (i.e. precipitate) and therefore trigger coke formationprocesses.

From a physico-chemical point of view, the phase separation phenomenoncan be explained by the fact that the asphaltene phase becomes more andmore aromatic with the advancing of the conversion reactions, due to theeffect of the dealkylation and condensation reactions.

Consequently, beyond a certain level, the asphaltenes are no longersoluble in the malthene phase, also because, in the meantime, the latterhas become more “paraffinic”.

The control of the loss of stability of a heavy charge stock during athermal and/or catalytic conversion, is therefore fundamental forobtaining the maximum conversion degree without creating problems due tothe formation of coke or fouling.

In “once-through” processes, the optimum operative conditions (mainlyreaction temperature and residence time) are simply determined on thebasis of the stability of the reactor effluent through directmeasurements on the non-converted residue (P value, Hot Filtration Test,Spot Test, etc.).

All these processes allow more or less high conversion levels to bereached, according to the charge stock and the technology used, in anycase generating a non-converted residue at the stability limit, which wewill call tar, which, from case to case, can vary from 30 to 85% of theinitial charge stock. This product is used for producing combustibleoil, bitumens or it can be used as charge stock in gasificationprocesses.

Schemes have been proposed for increasing the overall conversion levelof cracking processes, which include the recycling of more or lesssignificant amounts of tar in the cracking unit.

In the case of hydroconversion processes with dispersed catalysts inslurry phase, the recycling of tar also allows the recovery of thecatalyst, to the extent that the same Applicants have described, inpatent application IT-95A001095, a process which allows the recycling ofthe catalyst recovered to the hydrotreatment reactor, without thenecessity of a further regeneration step, obtaining, at the same time, agood-quality product without the production of residue (“zero residuerefinery”).

This process comprises the following steps:

-   -   mixing of the heavy crude oil or distillation residue with a        suitable hydrogenation catalyst and sending the mixture obtained        to a hydrotreatment reactor, introducing into the latter        hydrogen or a mix of hydrogen and H₂S;    -   sending the stream containing the hydrotreatment reaction        product and the catalyst in dispersed phase to a distillation        zone in which the most volatile fractions are separated;    -   sending the high-boiling fraction obtained in the distillation        step to a deasphalting step and the consequent formation of two        streams, one consisting of deasphalted oil (DAO) and the other        consisting of asphalt, catalyst in dispersed phase and possibly        coke, and enriched with the metals coming from the initial        charge stock;    -   recycling of at least 60%, preferably at least 80%, of the        stream consisting of asphalt, catalyst in dispersed phase and        possibly coke, rich in metals, to the hydrotreating zone.

The same Applicants describe in the subsequent patent applicationIT-MI2001A001438 different process configurations with respect to thatdescribed above.

The process claimed therein by the combined use of the following threeprocess units: hydroconversion with catalysts in slurry phase (HT),distillation or flash (D), deasphalting (SDA), is characterized in thatthe three units operate on mixed streams consisting of fresh chargestock and recycled streams, using the following steps:

-   -   sending at least one fraction of the heavy charge stock to a        deasphalting section (SDA) in the presence of solvents,        obtaining two streams, one consisting of deasphalted oil (DAO),        the other of asphalts;    -   mixing the asphalt with a suitable hydrogenation catalyst and        possibly with the remaining fraction of the heavy charge stock        not sent to the deasphalting section and sending the mix        obtained to a hydrotreating reactor (HT), introducing into the        same reactor hydrogen or a mix of hydrogen and H₂S;    -   sending the stream containing the product of the hydrotreating        reaction and the catalyst in dispersed phase to one or more        distillation or flash (D) steps, whereby the most volatile        fractions are separated, among which the gases produced in the        hydrotreating reaction;    -   recycling of at least 60% by weight of the distillation residue        (tar) or of the liquid coming from the flash unit, containing        catalyst in dispersed phase, rich in metal sulphides produced by        de-metallation of the charge stock and possibly coke, to the        deasphalting zone.

With said configurations, the following advantages can be obtained:

-   -   maximation of the conversion yields into distillable products        (derivatives from both atmospheric and vacuum distillation), and        deasphalted oil (DAO), which, in most cases, can be over 95%        with respect to the charge;    -   maximation of the upgrading degree of the charge stock, i.e. of        the removal of the poisoning products present (metals, sulphur,        nitrogen, coal residue), minimizing the production of coke;    -   maximum flexibility in treating charges different by nature from        the hydrocarbon component (density) and level of the pollutants        present;    -   possibility of completely recycling the hydrogenation catalyst        without the necessity of regeneration.

The treatment of a heavy hydrocarbon charge stock by means of SolventDeasphalting allows the separation of two pseudo-componentsconventionally defined DeAsphalted Oil (DAO) and asphaltenes Cn (whereinn represents the number of carbon atoms of the paraffin used in thedeasphalting operation (normally from 3 to 6).

We have surprisingly found that if the DAO is subjected to ahydrotreatment section and the asphaltenes to a gasification section,the catalyst make-up is reduced, following the significant decrease inthe purging quantity necessary for removing the heavy metals (Ni, V, Fe,ect.) present in the feeding stream to the hydrotreatment itself.

The process, object of the present invention, for the conversion ofheavy and extra-heavy charge stocks by the combined use of at least thethree following process units: solvent deasphalting (SDA),hydroconversion with catalysts in slurry phase (HT), distillation orflash (D), is characterized in that it comprises the following steps:

-   -   sending the heavy charge stock to a deasphalting section (SDA)        in the presence of solvents, obtaining two streams, one        consisting of deasphalted oil (DAO), the other containing        asphaltenes;    -   mixing the stream consisting of deasphalted oil (DAO) with a        suitable hydrogenation catalyst precursor and sending the mix        obtained to a hydrotreatment reactor (HT), introducing into the        same, hydrogen or a mix containing hydrogen and H₂S;    -   sending the stream containing the product of the hydrotreatment        reaction and the catalyst in dispersed phase to one or more        distillation or flash (D) steps, whereby the most volatile        fractions are separated, among which the gases produced in the        hydrotreatment reaction, from the distillation residue (tar) or        from the liquid coming from the flash unit, containing catalyst        in dispersed phase, rich in metal sulphides produced by        de-metallation of the charge and possibly coke;    -   recycling of at least a portion of the distillation residue        (tar) or of the liquid coming from the flash unit, containing        catalyst in dispersed phase, rich in metal sulphides produced by        de-metallization of the charge and possibly coke, to the        hydrotreating section (HT).

The heavy charge stocks treated can be of a varying nature: they can beselected from heavy crude oils, distillation residues, heavy oils comingfrom catalytic treatments, for example “unconverted oils” from fixed orebullated bed hydrotreatment, “heavy cycle oils” from catalytic crackingtreatment, “thermal tars” (coming, for example from visbreaking orsimilar thermal processes), bitumens from “oil sands”, different kindsof coals and any other high boiling charge stock of a hydrocarbonorigin, normally known in the art as “black oils”.

The stream containing asphaltenes obtained in the deasphalting section(SDA) can be optionally mixed with the remaining part of thedistillation residue (tar), or the liquid coming from the flash unit,not recycled to the hydrotreatment section (HT).

Said stream containing asphaltenes, mixed or not mixed with part of thedistillation residue (tar) or of the liquid coming from the flash unit,can be:

-   -   sent to a gasification section (PO_(x)) so as to obtain a mix of        H₂ and CO;    -   sent to a coking or visbreaking section;    -   used for the formulation of fuels or as fuel for the production        of power used in cement works.

It is advisable for at least part of the distillation residue (tar) orliquid coming from the flash unit, preferably at least 80% by weight,more preferably at least 90% by weight, even more preferably at least99% by weight, to be recycled to the hydrotreatment section (HT),whereas the possible remaining part is sent to the gasification sectionPO_(x)). The gasification can be effected by feeding to the gasificationunit, in addition to the charge stock, oxygen and vapour which reactunder exothermic conditions at a temperature of over 1300° C. and apressure ranging from 30 to 80 bar, to produce mainly H₂ and CO.

A stream of syngas, or a mix of H₂ and CO, can be obtained from thegasification section, which can be further used as fuel by means ofcombustion with combined cycles (IGCC) or transformed into paraffinichydrocarbons by means of Fisher-Tropsch synthesis or converted intomethanol, dimethyl ether, formaldehyde and, more generally, into thewhole series of products deriving from Cl chemistry.

The same paraffinic hydrocarbons obtained via Fisher-Tropsch can bemixed with the various cuts obtained from the distillation or flashstep, improving their composition characteristics.

The catalyst precursors used can be selected from those obtained fromeasily decomposable oil-soluble precursors (metal naphthenates, metalderivatives of phosphonic acids, metal-carbonyls, etc.) or frompreformed compounds based on one or more transition metals such as Ni,Co, Ru, W and Mo: the latter is preferred thanks to its higher catalyticactivity.

The catalyst concentration, defined on the basis of the concentration ofthe metal or metals present in the hydroconversion reactor, ranges from350 to 30,000 ppm, preferably from 3,000 to 20,000 ppm, more preferablyfrom 5,000 to 15,000 ppm.

The hydrotreatment step (HT) is preferably carried out at a temperatureranging from 360 to 450° C., more preferably from 380 to 440° C., and ata pressure ranging from 3 to 30 MPa, preferably from 10 to 20 MPa.

Hydrogen is fed to the reactor, which can operate in both a down-flowmode and, preferably, up-flow. Said gas can be fed to several sectionsof the reactor.

The distillation steps are preferably effected under reduced pressure,ranging from 0.001 to 0.5 MPa, preferably from 0.1 to 0.3 MPa.

The hydrotreatment step (HT) can consist of one or more reactorsoperating within the condition range mentioned above. Part of thedistillates produced in the first reactor can be recycled to thesubsequent reactors of the same step.

The deasphalting step (SDA), effected by means of an extraction withsolvent, either a hydrocarbon solvent or not, is normally carried out attemperatures ranging from 40 to 200° C. and a pressure of 0.1 to 7 MPa.

It can also consist of one or more sections operating with the samesolvent or different solvents; the solvent recovery can be effectedunder sub-critical or supercritical multi-step conditions, thus allowinga further fractionation between the deasphalted oil and resins.

It is advisable for the solvent of this deasphalting step to be selectedfrom light paraffins having from 3 to 6 carbon atoms, preferably from 4to 5 carbon atoms, more preferably having 5 carbon atoms.

With the use of the gasification step (PO_(x)), in addition to obtaininga significant reduction in the purging quantity of the entire complex,there is the production of hydrogen, of which a portion can be adoptedfor the hydrotreatment reaction (HT).

In the process according to the invention a further secondary sectioncan be optionally present for the hydrogenation post-treatment of theC₂-500° C. fraction, preferably the C₅-350° C. fraction, coming from thesection of high pressure separators envisaged upstream of thedistillation.

In this case, before being sent to one or more distillation or flashsteps, the stream containing the hydrotreatment reaction product and thecatalyst in dispersed phase, is subjected to a separation pre-step,effected at high pressure, so as to obtain a light fraction and a heavyfraction, this heavy fraction alone being sent to said distillation (D)step(s).

The light fraction obtained from the high pressure separation step, canbe sent to a hydrotreatment section, producing a lighter fractioncontaining C₁-C₄ and H₂S gas and a less light fraction containinghydrotreated naphtha and gas oil.

The possible insertion of the secondary post-treatment hydrogenationsection of the C₂-500° C. fraction, preferably of the C₅-350° C.fraction, exploits the availability of this fraction together withhydrogen at a relatively high pressure, which is that of thehydrotreatment reactor, allowing the following advantages to beobtained:

-   -   fuels can be obtained, starting from oil charge stocks which are        extremely rich in sulphur, in line with the strictest        specifications on the sulphur content (<10-50 ppm of sulphur)        and improved as far as other characteristics of diesel gas oil        are concerned, such as density, poly-aromatic hydrocarbon        content and the cetane number;    -   the distillates produced do not suffer from stability problems.

The post-treatment hydrogenation on a fixed bed consists of thepreliminary separation of the reaction effluent of the hydrotreatmentreactor (HT) by means of one or more separators operating at highpressure and high temperature.

Whereas the heavy part, extracted from the bottom, is sent to the maindistillation unit, the aliquot which is extracted from the head, aC₅-350° C. fraction, is sent to a secondary treatment section in thepresence of hydrogen, available at high pressure, where the reactor isof the fixed bed type and contains a typicaldesulphurisation/dearomatisation catalyst, in order to obtain a productwhich having a considerably lowered sulphur content and also lowernitrogen contents, a lower total density and, at the same time,increased cetane numbers as far as the gas oil fraction is concerned.

The hydrotreatment section normally consists of one or more reactors inseries, the product of this system can be subsequently furtherfractionated by distillation to obtain a thoroughly desulphuratednaphtha and a diesel gas oil within specification as fuel.

The fixed-bed hydrodesulphurisation step, normally uses typicalfixed-bed catalysts for gas oil hydrodesulphurisation; said catalyst, orpossibly a mix of catalysts or a series of reactors with variouscatalysts having different properties, causes a deep refining of thelight fraction, significantly reducing the sulphur and nitrogen content,increasing the hydrogenation degree of the charge stock, thusdiminishing the density and increasing the cetane number of the gas oilfraction, at the same time reducing the formation of coke.

The catalyst normally consists of an amorphous part based on alumina,silica, silico-alumina and blends of different mineral oxides, on whicha hydrodesulphurizing component in association with a hydrogenatingproduct, is deposited (with several methods). Catalysts based onmolybdenum or tungsten with the addition of nickel and/or cobalt,deposited on a mineral amorphous carrier, are typical catalysts for thistype of operation.

The post-treatment hydrogenation reaction is effected at an absolutepressure slightly lower than that of the primary hydrotreatment step,normally ranging from 7 to 14 MPa, preferably from 9 to 12 MPa; thehydrodesulphurizing temperature ranges from 250 to 500° C., preferablyfrom 280 to 420° C.; the temperature normally depends on thedesulphuration level required. The space velocity is another importantvariable in controlling the quality of the product obtained: it canrange from 0.1 to 5 h⁻¹, preferably from 0.2 to 2 h⁻¹.

The quantity of hydrogen mixed with the charge stock is fed at aflow-rate ranging from 100 to 5,000 Nm³/m³, preferably from 300 to 1,000Nm³/m³.

An embodiment of the present invention is now provided with the help ofthe enclosed FIG. 1, which should not be considered as limiting thescope of the invention.

In FIG. 1 the heavy charge stock (1) is sent to the deasphalting unit(SDA): this operation is carried out by means of a solvent extractionoperation.

Two streams are obtained from the deasphalting unit (SDA): one stream(2) consisting of deasphalted oil (DAO), the other stream containingasphaltenes (3).

The stream containing asphaltenes (3) is sent to a gasification section(PO_(x)) in order to obtain syngas, i.e. a gaseous mix of H₂ and CO (4).

The stream consisting of deasphalted oil (2) is mixed with the freshmake-up catalyst (5) (necessary for reintegrating that lost with thestream (15) described hereunder) and with the stream (14) (describedhereunder) coming from the bottom of the distillation or flash column(D) to form the stream (6) which is fed to the hydrotreatment reactor(HT) into which hydrogen (or a mix containing hydrogen and H₂S) (7) isfed.

The hydrogen fed can be part of the hydrogen coming from thegasification step (PO_(x)) (not schematised in the figure)

A stream (8) leaves the reactor (HT), containing the hydrogenationproduct and the catalyst in dispersed phase, which is fractionated in adistillation or flash column (D) from which the lighter fraction (9)separates together with the distillable products (10), (11) and (12)from the distillation residue (13) containing the dispersed catalyst andcoke.

This stream (13) (called tar) is mostly recycled (14) to thehydrotreatment unit (HT), the remaining part (15) being sent to thegasification section (PO_(x)).

An example is provided for a better understanding of the invention, itbeing understood that the invention should not be considered as beinglimited thereto or thereby.

EXAMPLE 1

Following the scheme represented in FIG. 1, the followingexperimentation was carried out.

Deasphalting Step (SDA)

-   -   Charge stock: 250 g vacuum residue from Ural crude oil (Table 1)    -   Deasphalting agent: about 2.5 l of n-pentane    -   Temperature: 180° C.    -   Pressure: 16 atm.        The vacuum residue is charged into an autoclave together with a        volume of n-pentane equal to 8-10 times the volume of residue.        The mixture of charge stock and solvent is heated to a        temperature of 180° C., with stirring (800 rpm) by means of a        mechanical impeller for a period of 30 minutes. At the end of        the operation, decantation takes place and also separation        between the two phases, the asphaltene phase which is deposited        at the bottom of the autoclave and that of the deasphalted oil        diluted in the solvent. The decantation lasts for about two        hours. The DAO-solvent phase is transferred, by means of a        suitable recovery system, to a second tank. The DAOpentane phase        is then recovered, and the solvent is subsequently eliminated by        evaporation.

The yield obtained by the procedure described is equal to 82% by weightof deasphalted oil with respect to the starting vacuum residue.

The properties of the RV Ural and deasphalted oil (DAO C5) are shown intable 1. TABLE 1 Characteristics of the vacuum residue Ural 500° C. andDAO n-C5 extracted. C H N S CCR d²⁰ V Ni Charge (w %) (w %) (w %) (w %)(w %) (g/cm³) (ppm) (ppm) RV Ural 84.82 10.56 0.69 2.60 18.9 1.0043 26280 DAO C5 85.40 11.40 0.43 2.33 9.78 0.9760 71 23DAO Hydrotreatment Step

Catalytic tests were carried out using a stirred micro-autoclave of 30cm³, in accordance with the following general operative procedure:

-   -   about 10 g of the charge stock are introduced into the reactor        and the catalyst precursor is added;    -   the system is then pressurized with hydrogen and brought to        temperature by means of an electrically heated oven;    -   the system is maintained under stirring during the reaction by a        swinging capillary system operating at a rotational rate of 900        rpm; moreover, the total pressure is kept constant by means of        an automatic reintegration system of the hydrogen consumed;    -   quenching of the reaction is carried out once the test has been        completed; the autoclave is then depressurised and the gas        collected in a sampling bag; the gaseous samples are then sent        for gas-chromatographic analysis;    -   the products present in the reactor are recovered without the        addition of any solvent, and analyzed in terms of distribution        of the distillates, sulphur content, nitrogen content, coal        residue and metal content.

Hydrotreatment tests were effected using the DAO produced in thedeasphalting step, according to the following procedure. The reactor wascharged with DAO and the molybdenum compound and pressurized withhydrogen. The reaction was carried out under the operative conditionsshown in table 2, which indicates the data relating to the distributionof products and quality. TABLE 2 characteristics of the reaction productfrom the test according to Example 1 w % 420° C.; 3 hrs 420° C.; 5 hrs430° C.; 3 hrs Naphtha C5-170° C. 2.5 6.7 7.6 AGO 170-350° C. 22.2 29.532.8 VGO 350-500° C. 32.9 31.9 32.8 500° C. + 39.4 27.6 22.2 Gas (HC +H₂S) 3.0 4.3 4.6 S 0.79 0.44 0.48 N 0.35 0.30 0.33 Ni (ppm) 0.9 <0.5<0.5  V (ppm) 1.1 <0.5 <0.5

EXAMPLE 2

The following experimentation was carried out following the schemerepresented in FIG. 1.

Deasphalting Step (SDA)

Effected according to what is described in example 1.

Hydrotreatment Step

-   -   Reactor: 3,500 cc steel reactor equipped with magnetic stirring    -   Catalyst: 3,000 ppm of Mo/charge added using an or ganometallic,        oil-soluble precursor containing 15% w/w of metal    -   Temperature: 430° C.    -   Pressure: 16 MPa of hydrogen    -   Residence time: 3 hrs.

Using the DAO produced in the deasphalting step, hydrotreatment testswere performed according to the procedure described below. The reactorwas charged with DAO and the molybdenum compound and pressurized withhydrogen. The reaction was carried out under the operative conditionsdescribed. Quenching was effected once the test had been completed; theautoclave was depressurised and the gas collected in a sampling bag forgas-chromatographic analysis. The liquid product present in the reactorwas recovered and subjected to distillation in order to separate the500° C.+residue from the other distillation cuts. The distillationresidue (500° C.+) containing the catalyst, was charged again into thereactor and mixed with a suitable amount of DAO C5 previously prepared,in order to keep the quantity of the total charge stock constant. Thisprocedure was repeated until stabilization of the quantity of theresidue obtained, i.e. until stationary conditions were reached.

Distillation Step

-   -   Effected by means of laboratory equipment for the distillation        of oil charge stocks.        Results of the Experimentation        6 consecutive hydrotreatment tests of DAO C5 were carried out,        following the above-mentioned procedure. The ratio between the        quantity of recycled residue and the quantity of fresh charge        stock reached under these operative conditions was 0.47.

The data relating the outlet streams after the last recycling (% weightwith respect to the charge) are provided hereunder:

-   -   Gas: 4%    -   Naphtha (C₅-170° C.): 8%    -   Atmospheric gas oil (AGO, 170-350° C.): 27%    -   Vacuum gas oil (VGO, 350-500° C.): 31%

Vacuum residue (500° C.+): 30% TABLE 3 characteristics of the reactionproducts according to Example 2. Sulphur (w %) Nitrogen (ppm) Sp. Gr.(g/cm³) Naphtha C5-170° C. 0.03 300 0.7403 AGO 170-350° C. 0.11 18000.8451 VGO 350-500° C. 0.41 4400 0.9256

1. A process for the conversion of heavy charge stocks selected fromheavy and extra-heavy crude oils, distillation residues, heavy oils fromcatalytic treatment, thermal tars, bitumens from oil sands, carbons ofdifferent origins and other high boiling charges of a hydrocarbon originknown as “black oils”, by the combined used of at least the threefollowing process units: solvent deasphalting (SDA), hydroconversionwith slurry phase catalysts (HT), distillation or flash (D),characterized in that it comprises the following steps: sending theheavy charge stock to a deasphalting section (SDA) in the presence ofsolvents, obtaining two streams, one consisting of deasphalted oil(DAO), the other containing asphaltenes; mixing the stream consisting ofdeasphalted oil (DAO) with a suitable hydrogenation catalyst precursorand sending the mix obtained to a hydrotreatment reactor (HT),introducing into the same reactor, hydrogen or a mix containing hydrogenand H₂S; sending the stream containing the product of the hydrotreatmentreaction and the catalyst in dispersed phase to one or more distillationor flash (D) steps, whereby the most volatile fractions are separated,among which the gases produced in the hydrotreatment reaction, from thedistillation residue (tar) or from the liquid coming from the flashunit; recycling of at least a portion of the distillation residue (tar)or of the liquid coming from the flash unit, containing catalyst indispersed phase, rich in metal sulphides produced by de-metallization ofthe charge and possibly coke, to the hydrotreatment section (HT).
 2. Theprocess according to claim 1, wherein the stream containing asphaltenesobtained in the de-asphalting section (SDA) is mixed with the remainingpart of the distillation residue (tar) or the liquid coming from theflash unit which was not recycled to the hydrotreatment section (HT). 3.The process according to claim 1 or 2, wherein the stream containingasphaltenes obtained in the de-asphalting section (SDA) is sent to agasification section (PO_(x)) in order to obtain a mix of H₂ and CO. 4.The process according to claim 1 or 2, wherein the stream containingasphaltenes obtained in the deasphalting section (SDA) is sent to acoking or visbreaking section
 5. The process according to claim 1 or 2,wherein the stream containing asphaltenes obtained in the de-asphaltingsection (SDA) is used for the formulation of fuels or as fuel for powerproduction or is used in cement works.
 6. The process according to claim3, wherein the gasification is effected by feeding to the gasificationunit, in addition to the charge stock, oxygen and vapour which reactunder exothermic conditions at a temperature of over 1300° C. and apressure ranging from 30 to 80 bar, to produce mainly H₂ and CO.
 7. Theprocess according to claim 1, wherein at least 80% by weight of thedistillation residue (tar) or the liquid coming from the flash unit isrecycled to the hydrotreatment section (HT).
 8. The process according toclaim 7, wherein at least 90% by weight of the distillation residue orthe liquid coming from the flash unit is recycled to the hydrotreatmentsection (HT).
 9. The process according to claim 8, wherein at least 99%by weight of the distillation residue or the liquid coming from theflash unit is recycled to the hydrotreatment section (HT).
 10. Theprocess according to claim 3, wherein part of the hydrogen obtained fromthe gasification section (PO_(x)) is sent to the hydrotreatment (HT)step.
 11. The process according to claim 1, wherein the distillationsteps are carried out at reduced pressure, ranging from 0.001 to 0.5MPa.
 12. The process according to claim 11, wherein the distillationsteps are carried out at reduced pressure, ranging from 0.01 to 0.3 MPa.13. The process according to claim 1, wherein the hydrotreatment (HT)step is carried out at a temperature ranging from 360 to 450° C. and ata pressure ranging from 3 to 30 MPa.
 14. The process according to claim13, wherein the hydrotreatment (HT) step is carried out at a temperatureranging from 380 to 440° C. and at a pressure ranging from 10 to 20 MPa.15. The process according to claim 1, wherein the deasphalting (SDA)step is carried out at temperatures ranging from 40 to 200° C. and apressure ranging from 0.1 to 7 MPa.
 16. The process according to claim1, wherein the solvent of the deasphalting step (SDA) is a lightparaffin with a number of carbon atoms ranging from 3 to
 6. 17. Theprocess according to claim 16, wherein the deasphalting solvent is alight paraffin with a number of carbon atoms ranging from 4 to
 5. 18.The process according to claim 1, wherein the deasphalting (SDA) step iseffected with recovery of the solvent in supercritical phase.
 19. Theprocess according to claim 1, wherein, before being sent to one or moredistillation or flash steps, the stream containing the hydrotreatmentreaction product and the catalyst in dispersed phase, is sent to aseparation pre-step carried out at high pressure so as to obtain a lightfraction and a heavy fraction, said heavy fraction alone being sent tosaid distillation (D) step(s).
 20. The process according to claim 19,wherein the light fraction obtained by means of the high pressureseparation step, is sent to a secondary post-treatment hydrogenationstep, thus producing a lighter fraction containing C₁-C₄ gas and H₂S anda heavier fraction containing hydrotreated naphtha and gas oil.
 21. Theprocess according to claim 20, wherein the post-treatment hydrogenationreaction is effected at a pressure ranging from 7 to 14 MPa.
 22. Theprocess according to claim 1, wherein the hydrogenation catalyst is aneasily decomposable precursor or a preformed compound based on one ormore transition metals.
 23. The process according to claim 22, whereinthe transition metal is molybdenum.
 24. The process according to claim1, wherein the catalyst concentration in the hydroconversion reactor,defined on the basis of the concentration of the metal(s) present,ranges from 350 to 30,000 ppm.
 25. The process according to claim 24,wherein the catalyst concentration in the hydroconversion reactor rangesfrom 3,000 to 20,000 ppm.
 26. The process according to claim 25, whereinthe catalyst concentration in the hydroconversion reactor ranges from5,000 to 15,000 ppm.